See how your savings grow over time with compound interest. Add monthly contributions to watch your wealth accelerate.
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This compound interest calculator projects how a lump sum and regular monthly contributions grow over time, showing your final balance, total contributions, and interest earned with a clear year-by-year breakdown.
Compound interest is the engine behind long-term saving and investing: each period the interest you earn is added to your balance, so future interest is calculated on a larger and larger amount. Enter your starting principal, an expected annual rate, how often interest compounds (daily, monthly, quarterly, or annually), and the number of years, and the tool instantly returns the projected balance. Add an optional monthly contribution and you can watch how steady deposits accelerate growth far beyond what the initial principal alone would produce. People use it to:
The year-by-year table lets you see exactly when interest starts to outweigh your own deposits, which is often the most motivating moment in a long savings plan. Every calculation runs locally in your browser using the standard compound interest formula, so nothing you type is uploaded or stored anywhere. Results are gross projections meant for planning and education, not financial advice, so remember to allow for tax and inflation when judging real returns.
Interest calculated on both the initial principal and the interest accumulated from previous periods. Unlike simple interest, it grows exponentially.
Over long horizons, a lot. Each new contribution starts compounding immediately, so regular small deposits often end up worth more than the initial principal.
No. The calculator shows gross growth. Subtract tax on interest (or capital gains) for an after-tax projection.
Yes, though the difference is modest. Daily compounding earns slightly more than monthly, and monthly beats annual, because interest is added to the balance more often and so starts earning interest sooner. The gap widens over long time horizons and at higher rates, but it is usually small compared with the impact of the rate itself and your contributions.
APR (annual percentage rate) is the plain yearly rate before compounding is applied, while APY (annual percentage yield) folds in the effect of compounding to show the true yearly return. For example, 12 percent APR compounded monthly works out to roughly 12.68 percent APY. When comparing savings products, the APY is the figure that reflects what you actually earn.
The standard formula is A equals P times (1 plus r divided by n) to the power of n times t, where P is the principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the number of years. This tool applies that formula and, when you add a monthly contribution, also sums the future value of each deposit.
A quick estimate is the Rule of 72: divide 72 by your annual interest rate to get the approximate number of years to double. At 6 percent that is about 12 years, and at 8 percent about 9 years. For a precise figure, enter your numbers above and read the year-by-year table to see when the balance reaches twice your principal.